Various devices have been proposed to achieve the object of demobilizing a vehicle if the intending driver is intoxicated and thus "alcohol free" conditions are not present. Various such devices are taught in U.S. Pat. Nos. 3,855,573 3,815,087 3,824,538 3,823,382 and other U.S. Pats. recorded as references in one or more of the above U.S. Patents. In addition there is Australian Letters Patent No. 516365. A limitation that arises from such known devices is the inconvenience that can result in using a vehicle equipped therewith and accordingly, as a matter of choice, tends to be unacceptable. The inconvenience and/or unacceptability arises not only from the integrity of the device in fulfilling its role but also from the necessity of having to use the device at times when there is no likelihood of an intending driver being intoxicated. As a general rule such conditions prevail for a substantial period of time during which a vehicle is likely to be used. A further object of this invention is to provide a device which will overcome this problem or at least reduce it to a level so as to render the device acceptable or at least not particularly inconvenient to use.
Further problems arise with known devices as regards their sensitivity or lack of sensitivity. In the former case the presence of alcohol in the ambient air can render a device susceptible to spurious operation. On the other hand if a device is lacking in sensitivity considerable exhalation may be required from an intending user before the device has sufficient input to make the selection required of it. The device of Australian Patent 516365 has attempted to overcome this problem by providing that the alcohol sensor thereof is normally isolated from the ambient air. An air pressure operated sealing unit must be activated by a user's exhalation before the sensor is exposed to a breath sample.
Such an approach can lead to another problem associated with known devices being that of condensation and more particularly the desirability of achieving ready evaporation of condensation. Residual condensation can result in a false reading and/or delay while sufficient evaporation takes place to revert to a normal stable state.
Further, as a general rule, available alcohol sensors are susceptible to change resulting from change in ambient temperature and/or ambient humidity. This can render the threshold point associated with the sensor in determining "alcohol free" breath or otherwise inconsistent and thus the reliability of the device can be called into question.
A further object of this invention is to limit the problems associated with humidity and temperature whether they be those arising from instant use and/or from ambient conditions.